The present invention relates generally to coordinated multipoint (CoMP) transmission for the downlink in a mobile communication network and, more particularly, to a method and apparatus for computing precoding weights for a CoMP transmission in a distributed manner to reduce interference between neighboring CoMP cells.
The phenomenal growth in the demand for wireless communications has put a persistent pressure on cellular network operators to improve the capacity of their communication networks. To improve the spectral efficiency of these networks, scarce radio resources have to be reused aggressively in neighboring cells. As a result, inter-cell interference has become a main source of signal disturbance, limiting not only the service quality to users at the cell edges, but also the overall system throughput.
Coordinated Multi-Point (CoMP) transmission (or reception) is one technique being employed to mitigate inter-cell interference. The basic idea behind CoMP on the downlink is to connect multiple base-stations from several adjacent cell sites to a centralized processing unit (CPU), thus forming a “super-cell”, called a CoMP cell, such that transmissions to multiple user equipments (UEs) within each CoMP cell can be coordinated to reduce mutual interference among UEs. However, there is little or no coordination among CPUs of different CoMP cells in such a centralized architecture.
In the conventional centralized CoMP architecture, the users near the edge of a CoMP cell can experience substantially degraded service quality compared to those near the center of the CoMP cell due to the uncoordinated interference from other neighboring CoMP cells. This interference creates a large service quality disparity among users in the network. In fact, one can view that the centralized CoMP architecture is essentially the same as the traditional non-CoMP architecture except that the CoMP cells are larger and that the network antennas are distributed more evenly throughout each CoMP cell.
In order to reduce the portion of users being adversely affected by the uncoordinated inter-CoMP-cell interference, the number of cells included in each CoMP cell has to be large, posing difficult problems in synchronization due to signal delays over both the air and the wire. In addition, the cost increase in building and maintaining the backhaul connecting a large number of cell sites to the CPU in a large CoMP cell can also be substantial. Moreover, the centralized architecture is not easily scalable to future traffic increase in each CoMP cell, since adding a new cell-site requires a new backhaul connection to the CPU and a change in the processing algorithms at the CPU to accommodate the new site.